A tissue is said to be differentiated when it has begun to synthesize characteristic macromolecules specific for that tissue. In some tissues, specific proteins have been well characterized and their appearance during histodifferentiation can be monitored and assayed in minute quantities. In keratinizing epithelium the pattern of appearance of constitutive proteins during differentiation has been monitored in experiments with skin, but this approach to the study of oral epithelium has not been made. In this proposal, we plan to analyze the dorsal tongue epithelium of the rat during development by morphological and biochemical methods. A serial study of the epithelium as it differentiates from the 12th fetal day to mature keratinizing filiform papillae will be done by electron microscopy. In the same age groups, the constitutive proteins of the lingual epithelium will be analyzed biochemically with SDS-polyacrylamide gel electrophoresis which will yield quantitative and qualitative information on the proteins important in keratinization and will characterize them according to molecular weight. For each developmental stage, the protein profile will be correlated with morphological findings. These data will contribute to the correlation between the structure and biochemistry of oral epithelium. The major significance of this work is that it could form the basis for a biochemical classification of both healthy and diseased tissues by their constitutive protein profiles.